Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $51.95   13.311%   $58.8651   $58.87   $58.85   $58.90  
  Purchase #2 $233.84   11.871%   $261.5991   $261.60   $261.60   $261.60  
  Purchase #3 $171.86   6.686%   $183.3506   $183.35   $183.35   $183.40  
  Purchase #4 $213.39   6.854%   $228.0158   $228.02   $228.00   $228.00  
  Purchase #5 $14.35   11.593%   $16.0136   $16.01   $16.00   $16.00  
  Purchase #6 $230.37   9.418%   $252.0662   $252.07   $252.05   $252.10  
  Purchase #7 $152.77   9.723%   $167.6238   $167.62   $167.60   $167.60  
  7 purchase totals = $1,068.53       $1,167.5342   $1,167.54   $1,167.45   $1,167.60